1. Field of the Invention
The present invention relates to a method for manufacturing an electron source substrate to be used in an electron beam device and an image forming device such as an image display device or an application of the electron beam device.
2. Description of the Related Art
The electron source substrate of this kind is provided with a plurality of electron emission elements constructing an electron emission portion. As the electron emission elements, there are generally known two kinds a thermal electron source and a cold cathode electron source. The cold cathode electron source is divided into a field emission element (FE element), a metal-insulator-metal element (MIM element), a surface-conduction electron-emitting element (SCE element), and so on.
FIG. 16 is a diagram showing an element construction of M. Hartwell as a typical element construction of the surface-conduction electron-emitting element. In FIG. 16: numeral 1 designates a substrate; numerals 2 and 3 element electrodes; numeral 4 a conductive thin film; and numeral 5 an electron emission portion.
The surface-conduction electron-emitting element thus constructed has an especially simple structure of the cold cathode electron source and can be easily manufactured. Therefore, the surface-conduction electron-emitting element has an advantage that a multiplicity of elements can be formed over a wide area.
The application of the surface-conduction electron-emitting elements has been investigated to find an image forming device such as an image display device or an image recording device, or a charge beam source.
Especially as the application to the image display device, there has been investigated an image display device that combines the surface-conduction electron-emitting elements and a fluorescent member for emitting a light when irradiated with an electron beam, for example, as disclosed in U.S. Pat. No. 5,066,883. The image display device using the surface-conduction electron-emitting elements and the fluorescent member in combination has characteristics superior to those of image display devices of other types in the conventional art.
As compared with a liquid crystal display device, which has become more widespread in recent years, for example, the above-mentioned device is superior in that it requires no back light because it is of a self luminescence type and in that it has a wide angle of view. Because of the simple structure, moreover, the above-mentioned image display device is expected to be applied especially to image forming devices having a large area.
In the image forming device having a large area, generally speaking, there is frequently adopted the construction in which a spacer is arranged between a rear plate having an electron source substrate and a face plate having a fluorescent member or an anode member. The space between the rear plate and the face plate is made to be a vacuum so that the atmospheric pressure may be supported by the spacer having a sufficient mechanical strength thereby to keep the plate distance constant. The role of the spacer is the more important as the screen of the image forming device has the larger area.
Here, this spacer may exert influences on the orbits of electrons to fly between the rear plate and the face plate. The cause for influencing the electron orbits is the charge of the spacer. This spacer charge is thought to result either because a portion of the electrons emitted from the electron source or the electrons reflected on the face plate come into the spacer so that secondary electrons are emitted from the spacer, or because the ions ionized by the collisions of the electrons attach to the spacer surface.
When the spacers is positively charged, the electrons flying near the spacer are attracted by the spacer so that the display image is distorted near the spacer. The influences of this charge become the more prominent as the distance between the rear plate and the face plate becomes larger.
As methods for preventing this problem, there have been known a method for forming electron orbit correcting electrodes at the spacer and a method for removing the charges by making the charge face conductive to feed a little current.
The Applicant has investigated the application of the technique of an ink jet device to the manufacture of the electron source substrate having the surface-conduction electron-emitting elements. In this technique, a metal-containing solution is applied in the state of liquid droplets to a substrate thereby to form a conductive thin film, and an electron emission portion is formed in the conductive thin film. Then, an electron source substrate of a large area can be manufactured at a high throughput by applying a plurality of liquid droplets simultaneously with an ink jet device having a plurality of nozzles.
However, the following problems are left unsolved in the aforementioned manufacturing method.
The nozzles belonging to the ink jet device are not always constant in their distances. Therefore, the individual nozzles are different in the liquid droplet application position (i.e., the drop placement) of the metal-containing solution. As a result, the positions of the electron emission portions to be manufactured may vary, resulting in a degradation of the image quality. If this variation occurs, especially at such a portion of the screen that displays important information, e.g., the central portion of the screen, the degradation of the image quality is easily recognized, causing a problem for the display device. In the case of the aforementioned display device using the spacer, on the other hand, even slight positional displacement of the electron emission portions near the spacer at the time of manufacturing exerts serious influences on the electron orbits, thereby distorting the display image, so that the image quality is seriously degraded.
In order to avoid these disadvantages, therefore, it is conceivable to form the electron source substrate of a large area by using an ink jet device having an extremely high accuracy, which has little difference in the liquid droplet applying positions of the individual nozzles. In this case, however, the production yield of the ink jet device itself drops so that the cost for the electron source substrate also rises disadvantageously.
In EP 869528 A (corresponding to JP-A-H10-334837), moreover, the Applicant has clarified that the distortion of the display image can be eliminated by adjusting the arrangement distance of the electron emission portions near the spacer. For example, in case the conductive thin films are to be formed as a whole by the ink jet device having a plurality of nozzles, however, the positions of the electron emission portions cannot be individually controlled, making it difficult to form the electron source substrate of a high quality at a high throughput.